Medical consultants in the field of ophthalmology often require an indication of the quality of the visual response of various parts of the retina in a patient's eye as this can often provide an indication of the presence or progress of at least three conditions, these being glaucoma, retinitis pigmentosa and, in some cases, multiple sclerosis. All three of these conditions have been known to cause permanent blindness.
Of these three conditions, only glaucoma is at the present time treatable with success. However, early detection of this condition is very important.
One of the earliest symptoms which can be detected is a reduction in the response of the eye to low levels of illumination. Current apparatus to test the field of vision by testing the response of different parts of the retina to low levels of illumination comprises a large, heavy and bulky piece of equipment. A patient is made to sit placing his or her head in a hemispherical screen in a dimly lit room. A light of varying brightness is projected at different points on the screen and the patient is asked to press a button each time a point of light is seen. The responses to the different points of light together with the minimum level of brightness required for detection are stored and printed out on a response map at the end of the test. All, or only selected parts, of the eye may be mapped in this way.
However, the process, which may take fifteen minutes or more, is uncomfortable for the patient and may lead to cramps or stiffness in the neck and back. In addition, only one eye may be tested at a time. The dim lighting required in the room presents problems for patients with poor vision and the need for a physical response can also lead to inaccurate results when testing unreliable patients such as older patients, children or those with very low mental capabilities.
The known apparatus which comprises an expensive and heavy electromechanical device has to be permanently located in one place and requires precise adjustment if the results are to be accurate. In addition, the patient must be reasonably fit physically in order to participate in the test. For example, the test cannot be performed very well for anyone who is unable to sit in one position without serious discomfort for fifteen minutes or more, such as patients suffering with arthritis, slipped discs, wheelchair users or those confined to bed.
Accordingly, it is an object of the present invention to provide apparatus and a method for testing the visual response of a patient in which some or all of the aforementioned disadvantages are at least partly overcome.